1. Field of the Invention
The present invention relates to an impulse generator, and more particularly, to an impulse generator capable of selectively outputting one of negative and positive impulses, so as to improve reliability of the impulses and reduce power consumption.
2. Description of the Related Art
Related art ultra wide band (UWB) communication technology is a considerable next-generation wireless transmission technology achieving 100 Mbps of data transmission speed, which is much higher than the 54 Mbps transmission speed of the IEEE 802.11a standard, and consuming power below 100 mW, which is better than the low power property of the Bluetooth standard. The related art UWB communication technology uses a few GHz of frequency bandwidth, and obtains 500 Mbps to 1 Gbps of data transmission speed by the bandwidth.
The related art UWB communication technology does not use a carrier wave in data transmission and reception, but instead loads data on pulses. Each of the pulses used in data transmission and reception is comprised of 1 ns (nanosecond) to a few hundreds of ps (picoseconds) of ultrashort waves.
To generate the pulses, a related art UWB communication system uses an impulse generator as shown in FIGS. 1, 2A and 2B.
FIG. 1 is a circuit diagram illustrating one example of the impulse generator of the related art UWB communication system. The related art impulse generator generates impulses by instantaneous discharge using a transistor that is a semiconductor switching element. A capacitor CB is connected to the base of the transistor, and a DC supply source, a resistor Re and a capacitor CC are connected to the collector of the transistor. The capacitor CB connected to the base has relatively large capacity, and the capacitor CC connected to the collector has relatively small capacity.
When a square wave is input to the base of the transistor of the impulse generator, the transistor is transited to its on position, and current flows from the collector to the emitter. If a high voltage is applied to the resistor Re of the collector by the DC supply source, when the transistor is turned on, the voltage sharply falls. The impulse is instantaneously generated in the emitter by the voltage sharply falling in the collector. On the other hand, the width of the impulse varies according to the properties of the switching element used.
FIG. 2A is a circuit diagram illustrating another example of the impulse generator of the related art UWB communication system, and FIG. 2B is a graph showing flow of voltage and current input to the related art impulse generator of FIG. 2A.
As shown in FIG. 2A, the impulse generator includes a step recovery diode (SRD) and a pair of Schottky diodes D1 and D2. When the voltage flows forward, the SRD stores energy according to Kirchhoff's Law, and when the voltage flows backward, the SRD is maintained for a predetermined time by the energy, and then suddenly drops off. The pair of Schottky diodes D1 and D2 reduce the forward turn-on voltage to 0.2 to 0.3 V by using Schottky barriers, thereby minimizing power loss and achieving high speed operation.
In the impulse generator, when the forward voltage is supplied to the SRD and the backward voltage is supplied to the SRD, the SRD is maintained in the on position for a predetermined time and then suddenly drops off. When the voltage is sharply varied in the SRD, the Schottky diodes D1 and D2 directly discharge the supplied voltage. Therefore, the output voltage becomes zero. The impulses are generated by the output voltage that is directly discharged from the Schottky diodes D1 and D2.
FIG. 2B is a graph showing variations of the voltage and current of the related art SRD and generation of the impulse by variations of the voltage from the power supply source of the impulse generator. When the forward voltage is supplied from the power supply source Vin to the SRD and the backward voltage is supplied to the SRD, the current applied to the SRD flows in the backward direction for a predetermined time TD, and then suddenly flows in the forward direction. Here, TD represents the time for which the SRD maintains the on state due to the energy stored in the SRD and the capacitor, and TS represents the time required to change the backward direction to the forward direction, which is the time required to discharge the voltage from the Schottky diodes.
However, the impulse generators of FIGS. 1 and 2A only generate positive impulses due to the circuit properties. In addition, the impulse generators need power for the entire operation time, due to the properties of the transistor or the SRD, which increases power consumption.
FIG. 3A is a circuit diagram illustrating yet another example of the related art impulse generator, and FIG. 3B is a graph showing an input voltage, a current and an impulse input in the operation of the related art impulse generator. The impulse generator includes an SRD, and a transmission line branched between the SRD and the output terminal, and having its end shorted. Normally, the current is reflected in the transmission line. In the case of a radio frequency, if the end of the transmission is shorted, the Ringing phenomenon reflecting the current occurs.
When an input voltage VS is supplied to the impulse generator, the forward current iSR flows through the transmission line, and the backward current iSF is generated by reflecting the forward current iSR. Since the backward current iSF is generated by reflecting the forward current iSR, the backward current iSF has a predetermined width of a phase difference from the forward current iSR. Because of the phase difference, when the forward current iSR and the backward current iSF interfere with each other, the forward current iSR and the backward current iSF are not completely extinguished with respect to each other, but generate impulses. When the input voltage VS rectified in a pulse shape through the SRD is transited to its off position, a negative impulse is generated, and when the input voltage VS is transited to its on position, a positive impulse is generated. In addition, the forward current iSR is not completely extinguished. Thus, unnecessary pulses are generated between the negative and positive impulses.
Since the related art impulse generator generates the negative and positive impulses, the related art impulse generator cannot selectively use one of the negative and positive impulses. Furthermore, unnecessary pulses are generated between the negative and positive impulses due to the Ringing phenomenon, which reduces the reliability of the impulses.
It is thus necessary to design the impulse generator which can selectively use one of the negative and positive impulses, obtain reliability of the impulses and reduce power consumption.